Toxic blue-green algae found at Pier 4 beach in Hamilton Harbour

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Toxic blue-green algae has been found at Pier 4 beach in Hamilton Harbour.

"Do not come into contact with the water," the city warned in a notice on its beach water quality monitoring webpage.

Richard MacDonald, manager of food and water safety at Hamilton Public Health Services, said the beach is closed.

"We are going to continue to monitor it weekly until we're confident, with the sample results in two weeks or so, that there is no more of the toxin-producing bacteria present," MacDonald told CBC News.

He said the algae was discovered during a routine observation by city staff on Monday, and tests later confirmed it's the blue-green kind.

Blue-green algae, also called cyanobacteria, are naturally occurring organisms found in bodies of water like lakes and ponds. 

Some blue-green algae blooms produce toxins that, when the blooms die, can be released into the water.

The toxins can be harmful to humans, causing symptoms like skin irritation and sore throat. If swallowed, they can cause liver damage, fever and diarrhea.

Hamilton Public Health Services monitors the recreational water quality at public beaches each year for levels of E. coli bacteria and blue-green algae. 

Blueish, greenish hue almost like gasoline

MacDonald said people going for a swim in other areas should observe the water before jumping in.

He said "a blueish, greenish hue almost like gasoline or like petroleum products on the surface" would indicate the presence of the algae.

"If people see that, particularly at a bathing beach, they can contact Public Health Services," MacDonald said.

"If they see it in other recreating areas … for instance Lake Ontario, Hamilton Harbour or any other body of water in and around the City of Hamilton … they can report those blue-green algae blooms to the Spills Action Centre."